Differences Between Crustaceans & Insects | Sciencing Differences Between Crustaceans & Insects By Steve Johnson Jupiterimages/BananaStock/Getty Images Along with arachnids, crustaceans and insects belong to the same group---arthropods. Sharing distinctive physical characteristics, such as absence of backbone, hard exoskeletons, jointed legs and segmented bodies, arthropods are easily distinguished from other animal groups. Although the arachnids are easily differentiated from other arthropods, the distinctions between crustaceans and insects are present, but a bit trickier to spot at times. Body Parts Differing mostly in their body parts, insects, such as ants, flies, wasps and dragonflies, have tri-segmented bodies consisting of the head, thorax and abdomen; crustaceans, such as crabs, lobsters, shrimps and crayfish, have only two body segments --- the head and thorax. These two segments fuse together into a cephalothorax and an abdomen. Insects have three pairs of legs attached to their thoracic region.

Crustaceans have more than three pairs of legs --- usually five pairs in most species; however, this is highly variable as many species have more pairs. Habitat and Related Adaptation Insects are found in almost all ecosystems on Earth, with the rarity being oceans. While some species, such as coconut crabs, sand hoppers, woodlice and pill bugs dwell on land, crustaceans are generally found in water --- and usually oceanic --- regions. Adapting to their habitat, many insect species evolved wings --- two pairs for most and one pair for others. A tracheal system is also present for breathing. Crustaceans, on the other hand, breathe using gill-like mechanisms. Other Differences Insects typically have a pair of antennae. Most crustaceans do not have antennae, but those that do, will have two pairs. Insects usually have mandibles for tearing food and helping in its digestion. Crustaceans have chelicerae, or claws, at the end of their first set of legs to do this same thing.

Insects Are Evolved Crustaceans Emphasizing more similarities than differences between insects and crustaceans, insects are closely related to crustaceans and often considered a land-dwelling version of them. Given common characteristics, such as the shedding of an exoskeleton and hatching from eggs, the accepted theory regarding differences between insects and crustaceans lay in genetic evolution. Some of the changes --- specifically the changes in segmentation --- are closely related to changes in Hox genes. References Crustacean - definition of crustacean by The Free Dictionary Crustacean - definition of crustacean by The Free Dictionary (krŭ-stā′shən) n. Any of various predominantly aquatic arthropods of the subphylum (or class) Crustacea, including lobsters, crabs, shrimps, and barnacles, characteristically having a segmented body, a chitinous exoskeleton, paired jointed limbs, and two pairs of antennae. [From New Latin Crūstācea, class name, neuter pl.

of crūstāceus, hard-shelled, from Latin crusta, shell; see kreus- in the Appendix of Indo-European roots.] crus·ta′cean adj. (krʌˈsteɪʃən) n (Animals) any arthropod of the mainly aquatic class Crustacea, typically having a carapace hardened with lime and including the lobsters, crabs, shrimps, woodlice, barnacles, copepods, and water fleas adj (Animals) of, relating to, or belonging to the Crustacea [C19: from New Latin crūstāceus hard-shelled, from Latin crūsta shell, crust] crus•ta•cean (krʌˈsteɪ ʃən) n. 1. any chiefly aquatic arthropod of the class Crustacea, typically having the body covered with a hard shell, including lobsters, shrimps, crabs, barnacles, and wood lice. adj. 2. belonging or pertaining to the Crustacea.

[1825–35; < New Latin Crustace(a) (see crust , -acea ) + -an 1] crus·ta·cean (krŭ-stā′shən) Any of various arthropods that live mostly in water and have a hard shell, a segmented body, and jointed appendages. Crustaceans include crabs, lobsters, shrimp, and barnacles. insect , spider , crustacean - One major difference between insects, spiders, and crustaceans is the antennae; most insects have one pair, spiders have none, and crustaceans have two pairs. See also related terms for spider .

ThesaurusAntonymsRelated WordsSynonymsLegend: crustacean - any mainly aquatic arthropod usually having a segmented body and chitinous exoskeleton arthropod - invertebrate having jointed limbs and a segmented body with an exoskeleton made of chitin class Crustacea , Crustacea - class of mandibulate arthropods including: lobsters; crabs; shrimps; woodlice; barnacles; decapods; water fleas green gland - one of a pair of glands (believed to have excretory functions) in some crustaceans near the base of the large antennae malacostracan crustacean - a major subclass of crustaceans decapod , decapod crustacean - crustaceans characteristically having five pairs of locomotor appendages each joined to a segment of the thorax stomatopod , stomatopod crustacean - a kind of crustacean branchiopod , branchiopod crustacean , branchiopodan - aquatic crustaceans typically having a carapace and many pairs of leaflike appendages used for swimming as well as respiration and feeding copepod , copepod crustacean - minute

 marine or freshwater crustaceans usually having six pairs of limbs on the thorax; some abundant in plankton and others parasitic on fish mussel shrimp , ostracod , seed shrimp - tiny marine and freshwater crustaceans with a shrimp-like body enclosed in a bivalve shell barnacle , cirriped , cirripede - marine crustaceans with feathery food-catching appendages; free-swimming as larvae; as adults form a hard shell and live attached to submerged surfaces chela , nipper , pincer , claw - a grasping structure on the limb of a crustacean or other arthropods Adj.

Top 10 Arthropod Pets - Listverse Top 10 Arthropod Pets Amy Clark September 26, 2012 Arthropods have external skeletons, segmented bodies, and several jointed appendages. There are many different kinds of arthropods, including arachnids, insects, and crustaceans. Where some people regard these creatures as pests, others enjoy them as pets. The collection and keeping of these fascinating creatures is a growing hobby amongst many people. There are many sources for purchase, and quite a few forums dedicated to this most interesting field. Please be aware that not all of these are legal to own, and should not be released into the wild if they are not native to your area. The following lists ten common arthropod pets, in no particular order. 10 Walking Stick The walking stick, otherwise known as stick insect, stick bug, phasmids, ghost insects, or leaf insects, is an herbivore, living on leaves and other plant material. There are over 2,500 species. They are longer and thinner than the mantis, and are often confused as mantids.

Although they fall under the subclass pterygoda, meaning winged insect, they have no wings. They go through three life stages: the female drops many eggs that land wherever in the autumn, nymphs emerge in the spring, and by summer they are adults. The female can reproduce without males, and the offspring will be clones of the female. They survive by camouflaging themselves to look like the twigs and branches they perch on, even mimicking the color of said branch. As pets, they are easy to care for. Just try to imitate their natural environment with the proper humidity, temperature, and food. Handling is easy, as they are not aggressive, but are delicate and should be handled gently. The Indian walking stick is a popular classroom pet. They can be left alone for up to a week with no adverse affects. 9 Praying Mantis The praying mantis is so called because of its long spiked forelegs that are bent as if in prayer. Using these legs, the mantis lunges, grabs its prey, and holds it while eating it alive. They are predators, living on other insects, even cannibalizing one another at times.

They lay their eggs in the autumn in layered clusters, covered by a foam that hardens and is waterproof, hanging from a branch. In the spring, the tiny babies that survived by not being eaten by their siblings or other insects climb the branch and go through several metamorphosis until they are adults. With their final metamorphosis, they have wings. As pets, they are fun to watch. Feeding is generally easy, as they are aggressive and quick to snatch the offered food. Watching them eat may take a strong stomach, as the prey is alive and struggling through most of the ordeal. There are many different kinds of mantises in the pet trade, at all sorts of sizes. The largest mantis is the ischnomantis gigas, at a whopping 6 1/2 inches. The smallest is the bolbe pyhmaea, at about less than half an inch. It is well known that the female will eat the male during copulation. However, this does not always happen, especially if the female has been well fed prior. 8 Cockroach Most people think of roaches as pests. Yet only 5 or so out of 4,000 species of roaches are household pests.

Roaches adapt easily to their surroundings, although they are typically found in warm areas. They are mostly omnivores, but there are some species that eat wood. They are fast and very hardy, and can survive without food for a long time, without air for up to forty five minutes, and being submerged in water for half an hour. It is believed that roaches would survive a nuclear holocaust, and they certainly have a higher resistance to radiation than humans. As pests, they can leave trails of bacteria with their feces and cause allergic reactions in humans. But as pets, they are colorful, entertaining, and easy to care for. There are many beautiful specimens to choose from in the pet trade. The hissing cockroach is probably the most well known. Blaberus Craniifer, the true death head roach, is a lovely specimen that has the death head image on the back of its head. Feeding is simple, grind up some dry dog food and grain, or buy commercial roach jelly online. Misting is helpful, as some like to lick the drops off the side of the aquarium. Some are good climbers, and an inch of vaseline around the top of the aquarium will keep them inside.

They can be held easily, although you should wash your hands after. Breeding is easy, just keep a male and female together, and soon you will have lots of babies. The dubya roach is often used as a food source for other pet insects. 7 Beetles There are more than 350,000 species of beetles in the world, living in diverse places like deserts, tropical climates, and even in water. Some are pests that eat garden plants and some eat the pests, like aphids and mites, that eat garden plants. Some are useful in cleaning up carrion or dung. And some are eaten by other insects, animals, and birds. They lay eggs that hatch into larvae that can in some cases take years to become mature adults. The adults are generally not long-lived. In Japan, the rhinoceros beetle is a popular pet. They have a horn on the thorax and a horn pointing forward from the center thorax. They can reach almost 6 inches long and weigh 3 ounces. They can be purchased from stores and even vending machines. Sometimes they are used for gambling, fighting one another, as males tend to be combative.

The Goliath beetle is one of the largest and heaviest at up to 2 to 3 inches long and weighing a hefty 3 or 4 ounces. It belongs to the scarab family. The scarab family has some of the most beautiful markings and colors. Beetles are a little harder to find in the pet trade, and you may have to start with a larvae that will remain buried most of the time. But if you are patient, you will briefly have a fascinating pet. 6 Ants Ants are everywhere. They are predators, scavenger, and herbivores. They are very social and live in groups with a hierarchy. The colony is ruled by a queen, who is the only fertile female. The other, infertile females, are workers and soldiers. They communicate through pheromones, sounds, and touch and defend themselves by biting or stinging. They are related to wasps and bees. Some, like harvester ants are sold as food for pet horned lizards. Harvester ants are also sold for ant farms, a fun hobby many children and adults enjoy. Harvester ants have large jaws and will bite.

These farms are flat so the ants can be viewed as they go about their daily lives, building tunnels and carrying food. They should be fed a healthy diet of fruit, vegetables, birdseed or the white of a boiled egg. Special ant food can be ordered online. An eyedropper works well to deliver just a little bit of water to one area, not so much that any of the ants will drown. It is fun and educational to watch the socialization and teamwork of these enterprising creatures. It would be even more entertaining to watch them breed and raise babies, but queens are not usually offered as pets. For that, you may have to catch one. 5 Centipede Centipedes are fast and aggressive. They can be found in the tropics and in deserts. They hunt at night and eat roaches, crickets, mice and bats. If bothered, they will bite or pinch, and are venomous. They have flattened bodies, a single pair of legs per segment, and can get up to twelve inches long. There are over 8,000 species. These are pets for the advanced keeper. Care must be given that they do not escape. They are cannibalistic and must be housed separately.

Some can live more than a decade in the wild, and even longer as pets. Even though they can live in the desert, they require dark, damp habitats with plenty of hiding places. They molt seven to ten times before maturity. Centipedes do not have 100 legs like their name implies; rather they always have an odd number of legs. Usually the female of the species will grow larger than the male or have different colors. And while some people will hold their pet centipede, it is advisable not to. 4 Millipedes Unlike centipedes, millipedes are long, round, slow, and eat decaying vegetation. They also have 2 pair of legs per segment, as opposed to 1. They can have 36 to 400 legs, depending on the species. There are over 10,000 species. Millipedes burrow into the ground. Some may secrete a poison through their skin, and there are some mammals that get drugged off this secretion by licking the millipede. They defend themselves by curling into a ball and do not bite. Millipedes are easy to house and can live in groups.

The giant African millipede is a popular pet, getting as big as 10 inches. They can be long lived and are non aggressive, making them fun to hold. Pet millipedes will eat fruit or vegetables, and need extra calcium to aid in shedding. They like damp areas and live under plant debris, and need a somewhat deep substrate so they can burrow. Being nocturnal, they aren’t quite as visible as some pets, so you would want to watch them at night. They reproduce easily, so take care not to house males and females together if you don’t want a lot. While they are not aggressive, some people may have allergic reactions to their secretions and should take care. 3 Hermit Crabs Hermit crabs live in shells and as they grow change to newer, larger shells. The largest species can live 30 to 70 years or more. They are great climbers and diggers, and fun to watch. Some species live under water, like marine crabs, and others on land. Most are aquatic, living in saltwater, and even the land ones must return to the sea to breed.

There are many different colors, like red, brown, and purple, with varying patterns such as dots and stripes. They are scavengers and omnivores, eating dead things and plants. They are a popular pet, but many people do not realize how much care must be given to them. As a result, they are short lived as pets. They need space, proper substrate, fresh water, salt water, food, extra shells, and things to climb. For specifics, please go to the site mentioned above. If you want your hermit crab to live and be healthy, you must meet their specific needs. 2 Scorpions Scorpions are predators, eating other insects. They sting their prey to paralyze it before eating. There are over 2,000 species, and 30 or more have the venom that can kill a human. They grow from between 0.3 inches to 9 inches long. They have 8 legs, 2 claws that vary in size according to species, and a segmented tail with a stinger on the end. The emperor scorpion is probably the most common scorpion kept as a pet. They are black and have large claws, and grow to 6 inches.

Give them a place to burrow or hide, some crickets or roaches, proper heat and humidity, and a shallow water bowl. They can live 6 to 8 years, and shouldn’t be handled, although their venom isn’t as potent as other species. More than 1 can be kept together, as long as there are enough hiding spots and room to move. Since they are nocturnal, they will be more interesting to observe at night. 1 Tarantula This particular arthropod is my favorite. There are so many different sizes and color combinations and temperaments to choose from. Some have stripes like a tiger, and some have markings like a skeleton. Most are hairy. They can be found in America, Africa, Asia and Australia. The African and Asian tarantulas are known as old world, and typically have stronger venom and are more aggressive than the new world tarantulas found in America that usually will just flick irritating hairs when threatened. They eat quite a variety of living things, from crickets to mice. Some are arboreal, living high up in trees and others are terrestrial, living on the ground or in burrows. They are easy to find in the pet trade.

They range in size from a fingernail to a dinner plate. In an appropriate size enclosure, the burrowing species will dig and line a hole with webbing. Mine do this right up against the glass so I can always see them even when they are hiding. Feeding is entertaining. Drop the cricket or roach in and watch the tarantula dash out and grab it. The largest ones can be fed mice or rats, but it is unadvisable because the rodent might hurt the tarantula. Large dubya roaches work well for large tarantulas. Some tarantulas go long periods of time without eating, either because they simply aren’t hungry, or are getting ready to molt. That is also interesting, to peer into the enclosure and see what looks like 2 tarantulas! Because when they molt, they lay on their backs and step out of their old skin, leaving behind what looks like another whole tarantula. Don’t feed for a few days after molting as the tarantula is vulnerable and the fangs need to harden. More Great Lists Animal Groups Animal Groups Vertebrates and Invertebrates Warm-blooded animals regulate their own body temperatures; their bodies use energy to maintain a constant temperature.

Cold-blooded animals depend on their surroundings to establish their body temperatures. Almost all animals fall into one of two groups. Adult vertebrates have a spinal column, or backbone, running the length of the body; invertebrates do not. Vertebrates are often larger and have more complex bodies than invertebrates. However, there are many more invertebrates than vertebrates. Vertebrates Fish breathe through gills, and live in water; most are cold-blooded and lay eggs (although sharks give birth to live young). Amphibians are cold-blooded and live both on land (breathing with lungs) and in water (breathing through gills) at different times. Three types of amphibians are frogs and toads, salamanders, and caecilians. Caecilians are primitive amphibians that resemble earthworms. They are found in the tropics. Reptiles are cold-blooded and breathe with lungs. They have scales, and most lay eggs. Reptiles include snakes, turtles and tortoises, crocodiles and alligators, and lizards. Dinosaurs were reptiles, although some scientists believe that some were warm blooded. Birds are warm-blooded animals with feathers and wings.

They lay eggs, and most can fly (although many, including penguins and ostriches, cannot). Mammals are warm-blooded, and are nourished by their mothers' milk; most are born live (however, the platypus lays eggs). Most mammals also have body hair. Invertebrates Sponges are the most primitive of animal groups. They live in water (usually saltwater), are sessile (do not move from place to place), and filter tiny organisms out of the water for food. Coelenterates are also very primitive. Their mouths, which take in food and get rid of waste, are surrounded by stinging tentacles. Some coelenterates are jellyfish, corals, and sea anemones. Echinoderms include starfish, sea urchins, and sea cucumbers. They live in seawater and have external skeletons. Worms come in many varieties and live in all sorts of habitats — from the bottom of the ocean to the inside of other animals. They include flatworms (flukes), roundworms (hookworms), segmented worms (earthworms), and rotifers (philodina).

Mollusks are soft-bodied animals, which often live in hard shells. They include snails, slugs, octopus, squid, mussels, oysters, clams, scallops, chitons, and cuttlefish. Mollusks are the second-largest group of invertebrates, with 50,000 living species. Arthropods are the largest and most diverse of all animal groups. They have segmented bodies supported by a hard external skeleton (or exoskeleton). Arthropods include insects, arachnids (spiders and their relatives), centipedes, millipedes, and crustaceans like crabs, lobsters, and shrimp. Bug Types, Bugs, Museum Victoria, Australia MUSEUM VICTORIA download windows media Bug Types ‘Bug’ is a name that is given to many invertebrate animals, or animals that do not have a backbone. Mostly it is used to describe those invertebrate animals that have a segmented, hard outer skeleton and jointed legs. These animals are called arthropods and include insects, spiders, mites, scorpions, millipedes, centipedes and crustaceans.

Bugs are Arthropods Arthropods belong to the group or phylum Arthropoda, and their tough, armour-like covering is called an exoskeleton. The bodies of arthropods comprise several main divisions. Insects have three body divisions, spiders have two body divisions, while centipedes and millipedes have many small body divisions. Arthropods also have jointed legs. The number of legs and body divisions are used to classify bugs into smaller classes: Insects, Arachnids, Myriapods and Crustaceans. Insects Insects belong to the class Insecta. All adult insects have three body divisions, six legs and a pair of feelers, or antennae. The three body divisions of an insect are the head, thorax and abdomen. The head carries the eyes, the mouthparts and the antennae. The central body region, or thorax, has the legs attachedand wings, if there are any. The rear section, or abdomen, carries the insect's digestive and reproductive organs. Arachnids Spiders are not insects. They belong to the class Arachnida, which also includes scorpions, ticks and mites.

The bodies of arachnids are divided into two distinct regions. The head and thorax are fused together in the front section, called the cephalothorax, which attaches to the abdomen. All arachnids have eight legs attached to their cephalothorax, and all lack antennae and wings. Myriapods Centipedes and millipedes belong to the group Myriapoda. They have a pair of antennae, many small body segments and many legs. Centipedes and millipedes differ in that centipedes have one pair of legs per body segment while millipedes have two. Crustaceans Arthropods in the class Crustacea are mostly marine creatures, such as crabs and crayfish. While they are not generally called bugs, other crustaceans are. Slaters or woodlice are crustaceans. They have a variable number of legs (at least ten), two pairs of antennae, three body sections and limbs that branch in two Non-Arthropods Invertebrate animals that are soft-bodied and without legs are not usually considered to be bugs. Worms belong to a phylum called Annelida.

Slugs and snails belong to the phylum Mollusca. antenna: Biology of Animals & Plants - Arthropods Arthropods There was an earlier discussion about how the success of groups could be determined and compared. The arthropods , animals that have taken over almost all of the environments of the earth, could easily be given the top spot on the success pile. One piece of supporting evidence you might run across is that there are more species of arthropods than of all of the other multicelled animals combined, but that is only true for the described species, and more hobbyists have added to that list for insects (which are arthropods) than for any other group. No one knows how many species of roundworms there are, in contrast, because only a tiny group of researchers even care. Probably the most important feature of the arthropods in their exoskeleton , a complex rigid outside covering that gives the muscles something to pull against. Unlike a simple shell such as those of mollusks, an exoskeleton has many flexible joints, allowing a wide range of movement. Skeletons in our group are the "opposite" kind, endoskeletons .

There are advantages and disadvantages to the two skeletal systems: EXOSKELETONS More protective, covering the muscles and other soft tissues. Less protective, usually being under the muscles and soft tissues. Produces better leverage for the pull of muscles. Leverage is worse. As animals size increases, becomes impractically heavy - imposes size limitations, especially on land. Being internal, can support great size and weight without becoming itself too heavy. Once formed, does not grow; must be shed (molted), and animal must then rapidly "grow" (usually by taking in water or air) and produce a new, larger exoskeleton to "grow into." During molts, animals are extremely vulnerable. Grows fairly smoothly and evenly, no molting. As small animals, arthropods gain great advantages from their exoskeletons, including protection almost as good as an actual shell.

As anyone familiar with arthropod-based super heroes knows, arthropods are very strong for their size, but this is deceptive - this proportionate strength is a combination of better system leverage but mostly due to the fact that smaller muscles are proportionately stronger (a muscle half the size is much more than half as strong), and the basis of comparison, lifting X times ones own body weight, is easier if the body weight is very low. A spider or ant the size of a human would not even be strong enough to support its own weight. Dont tell the people who make science-fiction-horror movies. Land arthropods often produce exoskeletons out of materials that will still give support but which are relatively light, but even that keeps them from getting very big. So arthropods are very good as little animals, but have serious size limitations, which they make up for in numbers. Wherever you are, you are probably outnumbered by the arthropods in your immediate vicinity by hundreds, maybe thousands, to one.

It may be that arthropods are descended from some sort of segmented worm-type ancestor; in fact, a small phylum called the Onychophorans have many features of both groups, a few surviving species that appear as a blend or "link" might be expected to. Arthropods are segmented, at least as embryos, and commonly have antennae and chitinous mouthparts (chitin is a sort of hard but light protein-based material), also common in segmented worms. The two groups also have the same sort of nervous system . But where segmented worms have setae, arthropods have legs, sometimes lots and lots of them, sometimes modified to do some very un-leggy jobs, like manipulating food or pinching predators. Arthropod legs and other leglike appendages show a great deal of serial homology , a visible remnant of segmentation. It is common for subgroups of the arthropods to have characteristic numbers of legs, such as the decapods (10 legs), including crabs and lobsters, or the arachnids (8 walking legs), including spiders and scorpions, or the insects (6 legs).

There are not a lot of features that all arthropods have in common; beyond the couple just discussed, maybe there is only their open circulation system , where blood pushed by a heart just sort of percolates around through open spaces called sinuses. Such a system is somewhat limited for circulating oxygen, and higher-metabolism arthropods often have some sort of enhanced oxygen-carrying set-up: most insects, for example, have a tracheal system of tubes that connect every cell in the body to the outside air. The arthropod phylum is divided into two subphyla, named for a difference in mouthparts but with several other differences as well. The chelicerates , named for mouthparts derived from front legs and called chelicerae, do not have the mandibles or antennae found in the other subphylum. Chelicerates typically have six pairs of appendages: one pair is the chelicerae, followed usually by a pair of pedipalps , legs adapted for purposes other than walking, and then four pairs of walking legs.

The chelicerates include - - The horseshoe crabs , a very old group who have five pairs of walking legs and no pedipalps. From above, a horseshoe crab looks like a shield with two eyes and a tail; turned over , it looks a bit like the creatures that jump on peoples faces in the Alien movies (but is really much less nasty). Horseshoe crabs live in sandy tidal zones, where they have existed for a very long time looking much the same as they do today. Evolutionary theory would suggest that a creature very well-suited to an environment that has remained stable for a very long time would change very little, and this is certainly true of horseshoe crabs. In fact, when dosed with radiation or chemicals that would mutate most animals DNA, a horseshoe crab just fixes the damaged molecules - they actually have evolved systems that resist the changes that animals in less stable environments require to continue to survive. They also have some odd commercial uses.

- The arachnids , a land group made up of mostly predators, includes the scorpions , whose pedipalps are adapted into claw-like grabbers, chelipeds; the spiders , whose pedipalps are blunt and used as "feelers," and who make silk (even the ones that dont live in webs) and inject a combination of venom and digestive enzymes into their prey; the harvestmen , or "daddy longlegs," which are not really spiders although many folks think they are; the ticks and mites , small round-bodied animals. The ticks are virtually all parasites, and many of the mites are as well, although many mite species are free-living. Ticks are significant carriers of human diseases , and many humans develop allergies , "to dust," which are actually to mite droppings in the dust. The mandibulates , which have mandibles and antennae similar to those of segmented worms, are the other subphylum. The number and uses of their legs follows no set rule for the whole group, although subgroups of the mandibulates may have characteristic numbers of legs.

The mandibulates include - - The crustaceans , a huge and varied group that is mostly marine, but has many fresh water species and a handful of land species. One shared feature of this group is that their legs and leg-derived structures are somewhat forked (a trait called biramous appendages). Th e crustaceans include some familiar "shellfish," such as lobsters, crayfish, crabs, and shrimp, as well as many types of planktonic animals which float in the surface layers of large bodies of water. There is one species of tiny crustacean, with individuals distributed in the top layers of all the the worlds oceans, that is probably the species with more living individuals than any other. The land-living crustaceans are limited to damp environments, but include those animals commonly called pillbugs, potato bugs, wood lice or armadillo beetles. - The centipedes , a land group of poisonous predators with many legs, one pair on each segment. These often have warning colors such as red or orange and scurry off when youve turned over a rock. - The millipedes , a land group of plant-eaters with many legs, two pairs on each segment.

These slow-moving animals often have contrasting black warning markings, because when threatened they release poisonous cyanide gas. - The insects, a huge group, considered a land group although with a few fresh water species. These are such a part of human life that they get their own devoted section. Insect s have the traits already discussed for the arthropods and the mandibulates - exoskeleton (of chitin, a light material but very supportive if a structure is small enough - in some ways like fiberglass), open circulatory system, segmented worm-type nervous system, mandibles, antennae - and a few specific traits of their own. Insects typically are divided into three sections: a head, thorax, and abdomen. The thorax is where all of the structures used for movement are located: six walking legs (several types of mouthparts and perhaps other structures are built from what used to be legs, but only six real legs remain), and typically four wings. Insect s, unlike other winged animals, have not evolved their wings from pre-existing appendages, but rather from outgrowths of the thorax exoskeleton, possibly flaps that had been used to cover the gills of fresh water insects, or from the gills themselves.

The progression probably went from blunt gliding structures, through steerable glider wings, to flappable wings, to systems that can beat wings up to at least a thousand times a second. Many types of insects use only the back pair of wings for flying; the front pair in those insects have generally evolved into protective covers for the back wings. Insect s typically go through a limited number of molts (6 is the typical number) between hatching and adulthood, and with very few exceptions only develop fully-functional wings during the last molt. If you are looking at an insect with full wings, its almost certainly an adult and never going to get any bigger. Insects also go through two different pathways of development . In direct development (sometimes called simple metamorphosis), young insects look like miniature, wingless versions of the adults (these young are typically called nymphs). Crickets and grasshoppers develop this way. In indirect development (sometimes called complete metamorphosis), the larva is physically quite different from the adult. They often occupy different niches than adults as well, allowing more individuals to exist together in an ecosystem.

Larvae grow, molt, grow, molt, et cetera, until they encase themselves in a pupa form and completely reorganize themselves, a process called metamorphosis (sometimes breaking down to a "soup" of cells that then completely build a new individual) and emerge as adults. The terms "simple metamorphosis" and "complete metamorphosis" mentioned above can be confusing, and "metamorphosis" is usually just applied to animals that go through a major change. This is what butterflies do, as you probably know, but also beetles, bees, ants, and flies develop this way. In some cases, the adult acts almost exclusively to reproduce and spread offspring, not even being able to feed during their short time in that form. PRIMITIVE WINGLESS INSECTS - There are still some species of insects around descended from ancestors who never evolved wings. Most of these are small and, although youve been around them your whole life, you probably have never noticed them, except for maybe the insects commonly called silverfish , which encounter humans usually around drains.

PRIMITIVE WINGED INSECTS - Flying insects use two different drive systems in their wings - the more primitive system attaches directly to the inner ends of the wings, while the more modern drive a lever-and-pivot system built into the structure of the thorax. The primitive winged insects include the dragonflies , mayflies and damselflies (Odonata). MODERN WINGED INSECTS - These use the thorax drive system, which can produce wing beats so rapid that a special type of muscle had to evolve just to keep things moving. This group includes (these are only the well-known groups, there are several more) - - The grasshoppers and their relatives , which are obvious insects such as crickets and katydids and insects maybe not so obviously related, such as cockroaches , mantises , and walking sticks . These are direct developers. Orthoptera. - The "true bugs," which includes leaf hoppers and cicadas . These insects often seem more "boxy," with angles and straight lines. They are direct developers. Hemiptera. - The beetles , which have more named species than any other insect group.

These typically have hard shiny coverings, including front wings that cover and protect the back wings. They are indirect developers, often going through a grub or wormy larval stage. Coleoptera. - Butterflies and moths . Although usually moth wings fold back over the abdomen and butterfly wings dont , that is not a reliable way to tell them apart - there isnt really an easy way to do it, since there are some very mothlike butterflies and butterflylike moths. These are indirect developers, often caterpillars as larvae. Lepidoptera. - Flies . These roundish insects have only a single pair of wings, which often beat at extremely high speeds. The other pair of wings have evolved into short knobby structures (halteres) that beat opposite to the wings and counterbalance those forces. These are indirect developers, with often with soft wormy larvae , including maggots. Diptera. - Termites . These ant-like insects include the famous wood-eaters, which depend upon a whole ecosystem of unusual protozoans that live in their guts and actually digest the wood, but some termite species are mound-builders. They are indirect developers, with usually only reproductive adults having wings, and commonly exist in social colonies.

Isoptera. - Ants, Bees, and Wasps . Sometimes combined with the termites, these also are indirect developers and live in social colonies. Ants are ground foragers, bees are mostly plant eaters and wasps are mostly meat eaters. Hymenoptera. MODERN WINGLESS INSECTS . These insects show evidence of wings, so it is assumed that their ancestors were winged and evolution has led to the loss of the wings. Both of the types of insects in this group are commonly parasites for whom wings might interfere with staying on their host. This group includes the lice ( Phthiraptera and Psocoptera ) and the fleas ( Siphonaptera ). Building air conditioners and bridges. Waging war and taking slaves. Ranching and farming. Communicating precise directions to a food source. Awarding promotions based upon merit. All of these abilities have been observed in one or more of the social insects. Now, individual insects dont seem that brainy, but when you put them together in an organized colony, the collective seems to be smarter than the individuals.

This has been compared to how individual small bits of a large brain can work together to solve problems that each cannot handle on its own. It seems a very different system than the one found in larger animals, but may work more-or-less the same. And it may point the way to designing truly intelligent computers. In case you were wondering, termites construct elaborate structures to air condition their mounds, and bees use workers to both heat and cool hives. Ants will build bridges (and boats), sometimes out of the ants themselves, to cross obstacles. Ants also will send out purposeful raiding parties to other nests, bringing back larvae and pupae that as adults are permanently put to work on the "lowly" jobs that only the newly-emerged local adults do. They also confine, protect, and milk sugary food out of aphids (the ranching) and cultivate and fertilize fungus to eat (the farming). Bees returning from a foraging expedition perform a sound-and-touch "dance" to tell other bees where (in relation to the suns position) and how far away the food source is.

There is even some evidence that when another bee picks up this information, it has some idea of where exactly its going - if a researcher places a food source out in the middle of a pond, many bees seem to decide its not worth leaving the hive for. Although termites are born into their jobs and hold them their whole lives, several types of ants have a sort of promotion-track, where the more experienced ants are given more complicated jobs. Arthropods .. Arthropods (Insects, Spiders, etc.) This page will always be under construction! For a listing of our sources for all our pages on the Arthropods, for various valuable links to other websites, and for comments on the status of these pages, see the paragraph in blue at the bottom of this page. The phylum Arthropoda -- all those bilaterally symmetrical animals who possess external skeletons composed of chitin (a cellulose -- linear-chain hydrocarbon that forms a strong yet somewhat flexible shell), with segmented bodies and paired, jointed legs (insects, spiders, scorpions, crustaceans, centipedes, etc.) -- is far more diverse than are members of the chordate phylum to which all vertebrates including humans belong.

Indeed, the number of Arthropod species is far greater than those of all other phyla combined, and there are probably millions of species among the insects alone which have not yet even been identified and described. For a visual image of this varietal dominance, see this link: Group Diversity . The first creatures to leave the sea had shells made of chitin and had jointed legs (think of horseshoe crab-like creatures, the Euryptids or "sea-scorpions, who predate the earliest fishes), so they could move around on land and even breathe if their gill-plates stayed moist, though their size on land was limited by this kind of skeletal structure. Moreover, the importance of the Arthropods to our ecosystems is huge, despite their individually small sizes, and they may well be considered the most successful animals on the planet -- ancient and contemporary inhabitants of sea, land, and air. The Trilobites of the Cambrian Period (540 MYA) and later Paleozoic are perhaps the best-known ancestral form.

In our discussions of a very few examples of these creatures which follow in the pages linked below, we will try (over time) to build an understanding of them in light of their significance for our ecosystems. The classification we use here follows McGavin (cited below).

The phylum Arthropoda may be divided into two major subphyla: 1) Mandibulates -- those possessing antennae, and highly modified jaws for biting or chewing; these include a) Myriapods -- having 9 or more pairs of legs and two antennae, for example the Centipedes and Millipedes; b) Hexapods -- 6-legged arthropods having two antennae, including above all the class Insecta (the only winged arthropods) and also some related orders (Springtails and Bristletails); and c) Crustaceans -- mainly aquatic, having 4 antennae -- but including not only such ancient sea forms as barnacles, crabs, and shrimp but also such terrestrial isopods as the pillbug (found in our area); and the 2) Chelicerates -- with no antennae; they have"chelicerae" -- paired, jointed jaws that house fangs or pincer-like mouthparts -- and four pairs of legs.

These are prominently the Arachnids -- Spiders, Scorpions, Pseudoscorpions, mites & ticks-- as well as Horseshoe Crabs, Daddy Long-legs, and some extinct sea-scorpions. Below, click on the blue underlined headings to enter the relevant pages. 1) Mandibulates 1a) Myriapoda While some 800 species are known of other orders of Mandibulates who have 9 or more pairs of legs and two antennae, the Centipedes and Millipedes have some 13,000 species between them. The former are mostly nocturnal predators who use poisoned claws to kill prey, the latter eat mainly rotting organic matter or fungi. Crustaceans Crustaceans The major groups of Crustaceans Woodlouse or slater a land-living crustacean Crustaceans (make up a very large group of the Arthropods which include the crabs, lobsters, crayfish, shrimp, krill, barnacles brine shrimp, copepods, ostracods and mantis shrimp.

Crustaceans are found in a wide range of habitats - most are free-living freshwater or marine animals, but some are terrestrial (e.g. woodlice), some are parasitic (e.g. fish lice) and some do not move (e.g. barnacles). There are over 50,000 known species of crustaceans divided into a number of major groups - the Branchiopods, the Maxillopods, the Ostracods and the Malacostraca. The Malacostraca are further divided into five groups - decapods (e.g. crabs, lobsters and shrimp), stomatopods (mantis shrimp), euphausiids (krill), amphipods (e.g. sandhoppers) and isopods (land-based) crustaceans. Crustaceans are invertebrates with a hard exoskeleton (carapace), a segmented body that is bilaterally symmetrical, more than four pairs of jointed appendages ("legs") and an open circulatory system (the "blood" does not flow in a closed loop).

They also have eyes usually on stalks, a primitive ventral nerve cord and "brain" (ganglia near the antennae), a digestive system which is a straight tube for grinding food and a pair of digestive glands. Gills are used for respiration and they have a pair of green glands to excrete wastes (found near the base of the antennae). Features of Arthropoda Swimmerets Larva of a crab Most Crustaceans are either male or female and reproduce sexually. A small number, including barnacles, are hermaphrodites. In other species, viable eggs are produced by a female without needing to be fertilised by a male. In many decapods, the first one or two pairs of swimmerets are specialised for sperm transfer by the males and the females hold the eggs until they hatch into free-swimming larvae. In many species the fertilised eggs are just released into the water or attached to objects in the water. The larvae metamorphose through a number of stages before they become adults. Most Crustaceans are motile (able to move about independently) and can be herbivores, carnivores or detritvores. Some are parasites and live attached to their hosts (e.g.

fish lice). Diversity in Crustaceans Marine crustaceans have a very wide range of predators from mammals like sea otters and seals, other crustaceans, molluscs (e.g. octopuses), sea birds, fish and humans. They protect themselves by a variety of methods - their hard exoskeletons, their chelipeds, camouflage and rapid escape (burrowing or swimming away). Their sizes range from the Japanese spider crab with a leg span of 4.3 m to the smallest, a parasite of copepods, which is only 0.1 mm long. As a crustacean grows, its exoskeleton does not, so the animal must moult its old exoskeleton in order to house its expanding body. To prepare for moulting, the tissue layer under the exoskeleton detaches and secretes a new exoskeleton below the hard outer one. When the new exoskeleton is completely formed, the old exoskeleton splits along weak points and the animal pulls out, leaving its old exoskeleton intact except for the split. After a moult the animal must wait and often hide until the new exoskeleton hardens.

A crab with its discarded, smaller exoskeleton on the right

Question: What collective name is given to creatures with segmented bodies, such as insects, arachnids and crustaceans?
Answer: ARTHROPODS